Application of Bayesian nonparametric models to the uncertainty and sensitivity analysis of source term in a BWR severe accident

Zheng, X.; 伊藤 裕人; 川口 賢司; 玉置 等史; 丸山 結

Reliability Engineering & System Safety, 138, p.253 - 262, 2015/06

https://doi.org/10.1016/j.ress.2015.02.004

An important issue for nuclear severe accident is the source tern uncertainty and sensitivity analysis. Generally, thousands of cases are needed to reach a stable result of sensitivity analysis. Based on the limited data obtained by MELCOR analysis, in which the accident at Unit 2 of the Fukushima Daiichi Nuclear Power Plant is used as an example, an approximate stochastic model has been constructed via Bayesian nonparametrics, specifically, the Dirichlet process. The advantage of a nonparametric model is that any deterministic function between explanatory and response variables is not necessary to be determined. The complexity of model will grow automatically as more actual data is observed. The approximate model saves the computational cost and makes it possible to complement thousands of Monte Carlo computation for uncertainty and sensitivity analysis. Probability density functions of uncertainty analysis by MELCOR and the approximate model are obtained and compared. Two densities show great accordance that proves the good predictive ability of the stochastic model. The appropriateness of the approximate model is further validated by the cross-validation through the comparison with actual MELCOR results. Global sensitivity analysis by Sobol' sensitivity index has been performed with the approximate model. Three input parameters are ranked according to their respective influences on the output uncertainty based on first-order and total effect.

人工バリアに対する微生物の影響評価研究 成果概要

not registered

PNC TJ1150 94-004, 26 Pages, 1994/03

PNC-TJ1150-94-004.pdf:0.99MB

高レベル放射性廃棄物の地層処分の性能評価において微生物の影響を調べるため、各種微生物のアルカリ性(pH)及び還元性環境(Eh)に対する耐性を実験的に調査するとともに、微生物への核種の吸着の研究手法の調査をすることを目的とした。ガスを発生して核種の移行を促進する可能性があるメタン生成細菌(MPB)と、鉄やコンクリートの腐食を促進させるといわれる硫黄酸化細菌(SOB)について、ファーメンタ(発酵容器)を用いて35度C(MPB)、30度C(SOB)で培養した。活性を示すEh領域は、MPBはpH=8でEh=-210-230mV以下、SOBはpH=7.5でEh=+200+240mV以上であった。 またSOBは、pH=8以上では増殖しなかった。また、異なるEhと高pHに対する硫酸塩還元細菌(SRB)、MPB、SOBの適応性を比較した。さらに、SRBとSOBの相互関係と放射性元素及び重金属の微生物への吸着挙動について調査、検討した。